The Islamic State (IS) released a video Sunday that shows the murder of 21 Egyptian Coptic Christians who were kidnapped earlier this year in Libya.

The horrific footage, posted on an IS-affiliated Twitter feed, shows the simultaneous beheading of all 21 prisoners. The victims are shown on a beach in handcuffs and wearing orange jumpsuits. Their captors are dressed all in black with masks covering their faces.

The video, titled “A Message Signed With Blood to the Nation of the Cross,” claims to target the “hostile Egyptian church” to avenge “Muslim women persecuted by Coptic crusaders in Egypt.” The video was allegedly shot in Libya on “the coast of Wilayat Tarabulus by the Mediterranean Sea.”

In the footage, a masked militant addresses the camera, claiming that the when the blood of the Christians enters the sea it will be mixed with the blood of Osama Bin Laden. At the end, the camera pans out to show blood in the water. The militant finishes with a claim that the group will “conquer Rome.”